While searching, came across an old thread about removing these screws and noticed that I could not post a reply, probably due to the age of the thread. Anyway, I didn't see a suggestion to remove them that we have used several times on WC's, Dodge's and now our Kaiser. We try the penetrating oil, heat, impact drivers, etc., and when we cobble up a screw head so bad that we can't use a blade on it any more, we weld on a nut that is smaller than the head of the screw so that we don't accidentily weld to the brake drum face and let it cool and then just put a wrench on the nut and it comes out every time. Head up to ACE hardware and get all new screws. We put a little grease on them prior to assembly and hope the next time, they come off easier.
This technique also works on broken bolts or studs if you can get to the broken off part to weld a nut on. We have lucked out a few times on engine block head bolts that snap off a little above the block surface.